The developed test method exposes standard sized test specimens to systematic temperature and moisture variations over a time period up to 50 days. The bowing is measured during the testing period and provides a evaluation basis for the assessment of the stone materials risk of bowing and also information for the assessment of the stone panels durability in environments where the stone is used as cladding and is exposed to sun and rain (concerns almost all external claddings). The test method has been correlated to observations from the cladding of the structures and to petrographic examination of the microstructure and has shown a good correlation. The method should be able to provide a good and realistic assessment of a stone's tendency to deteriorate and bow on exterior claddings. In combination with non destructive (e.g. sound velocity) and/or destructive tests (e.g. flexural strength) additional durability data can be achieved. This test method is the first method for natural stones which provides data, that can be used for this assessment and will therefore be essential to guidelines, specifications and technical standards at European level. It has particular relevance to Directive Council Directive EEC 89/106 of 21 December 1988 on the approximation of laws, regulations and administrative provisions of the Member States relating to construction products. Decision makers, architects and building owners who select stones for claddings will need the results of this test method as a basis for their selection and the documentation of the durability. Such stones are currently selected, typically based on their appearance. Natural stone producers will have a major interest in having their stones tested or implement the test method them selves for Initial type testing or FPC in addition to other tests already specified and required for natural stones (water absorption, flexural strength, frost durability etc.)
The developed test method will be the first method that provides a correct assessment of the potential risk of irreversible thermal and moisture expansion of carbonate rocks. Existing methods are not applicable for marble and limestone. The results will provide information for the assessment of durability in use environments where stone slabs will be exposed to temperature and/or moisture gradients. This is of special importance in exterior claddings, where insufficient joint widths and movement allowance at fixings may give serious damages in the stone cladding. Decision makers, architects and building owners who select stone materials will need the test method and the results as a basis both for their material selection and construction design and also for the documentation of material behaviour and durability. Producers of marble and limestone will have a major interest in having their stones tested according to the method developed.
A prototype equipment for accurate measurements of the amount of bow on a façade clad was developed within a joint inter-Nordic project. The equipment called Bow-meter was improved and the design finalised within TEAM and the precision established and documented. The Bow-meter serves as a necessary equipment for repeated, low cost and non-destructive measurements of the continuous increase in bowing of facade claddings. Small changes can be measured from one year to the other and give the basis for a service life prediction. The procedure for façade assessment is really a methodology for an initial inspection that has proven to be very useful for all detailed inspections performed within TEAM and also at ordinary damage investigation commission work. The procedure also includes instructions for the use of the Bow-meter. The methodology is further developed into a comprehensive Guide describing inspection and risk assessment of facades. This work has already begun. The bow-meter itself has been produced in about 10 examples to this date. The handling is easy and it might therefore be produced in a larger quantity for self inspection by building owners or caretakers with problematic buildings.